1. Field of the Invention
The invention relates generally to an arrangement for varying the damping of a piston in hydraulic, pneumatic or hydro-pneumatic assemblies, such as vibration dampers, gas springs and hydro-pneumatic suspensions and, more particularly, to vibration dampers having the piston arranged to slide axially by means of a piston rod in a cylinder filled with at least one damping medium.
2. Description of the Prior Art
The prior art includes hydraulic shock absorbers, such as those disclosed in Federal Republic of Germany Patent Publication Published for Opposition Purposes No. DE-AS 12 42 945 and No. DE-AS 14 05 781, and French Patent No FR-PS 11 75 293, whose damping characteristics can be adjusted electromagnetically by changing the flow of the hydraulic damping medium through the damping valves. In these cases, there are two bypass connections, the first of which generally serves to regulate the damping force in the decompression stage in relation to the compression stage. To change the damping force to suit different road conditions, there is an additional bypass connection in the decompression stage, in which there is an electromagnetically-controlled valve. A disadvantage of this arrangement is that there is no way to control the damping force in the compression stage. In addition, with an electromagnet which can be turned either on or off, it is only possible to achieve a corresponding upper and lower damping force curve. In these systems, it is impossible to achieve intermediate values.
The prior art also includes hydraulic adjustable shock absorbers, such as in Federal Republic of Germany Laid Open Patent Application No. DE-OS 21 19 531, in which there is a first damping element and also a line equipped with a control valve. A control valve and a damping element are located separately in a closed loop. The setting of the control valve is done either manually or by the action of one of the vehicle mechanisms. A disadvantage of this arrangement is that when the control valve is activated, it is again only possible to achieve an upper and a lower damping force curve, whereby any damping values which may be desired between these two limit values cannot be achieved merely by turning on and off the control valve. Beyond the specified limits, there is no variability. The above-cited patent publications are incorporated herein by reference as if the contents thereof were fully set forth herein.